As a volume phase hologram, a white-light reconstruction hologram (a hologram reproducible by the light visible as white color by the naked eye, i.e., white light, the spectral distribution of which spreads over nearly the entire visible region), which is mainly used in security applications, and a Fourier transform hologram, which is used in data recording applications, have been proposed so far. These holograms are formed in separate recording media.
Meanwhile, there is a demand for a recording medium capable of recording both the white-light reconstruction hologram and Fourier transform hologram.
An exemplary application of this type of recording medium is that on one hand, the white-light reconstruction hologram guarantees the security of the recording medium, on the other hand, many data are recorded into this security guaranteed medium as Fourier transform holograms.
Holographic recording that records data as two-dimensional information is one of recording technology capable of storing large amounts of data and transferring the data at high speed. The holographic recording is performed in such a way that two-dimensional information is created by a spatial light modulator according to data to be recorded, after which it is condensed by a Fourier lens (Fourier-transformed) and guided to a recording medium as an object beam, where the object beam interferes with a reference beam.
In this process, for example, while sequentially changing the angle of the reference beam (angle multiplexing), the two-dimensional information created by the spatial light modulator is sequentially varied, whereby multiple two-dimensional information is recorded in a same volume in multiplexed form.
To reconstruct data recorded as holograms, a reference beam (or phase-conjugate beam) having the same condition as the one used when recording is irradiated to the recording medium to generate diffraction light, which is formed as a reconstructed image of the two-dimensional information through a Fourier lens. In contrast, white-light reconstruction holograms used in security and decoration applications include a type of holograms on which print materials and three-dimensional images are recorded by embossing its surface and other types, but all of these are recorded and reconstructed without performing a Fourier transformation. Accordingly, since the white-light reconstruction hologram and Fourier hologram differ from each other in their recording and reconstructing processes, it has been impossible to record both of them in a same recording medium.